摘要
作者用无液界电池电动势法测定了25℃恒离子强度(I=0.1,0.3,0.5和0.7)条件下KCl+KNO_3水溶液中KCl的平均质量摩尔浓度标度的活度系数,发现其活度系数的对数与混合溶液中KNO_3的浓度服从下列公式的关系: Lgγ1±=Lgγ_(1±)~0-a_(12)m_2-β12m_2~2且用最小二乘法求得了各离子强度条件下相应的哈奈特系数。还用Pitzer公式计算了混合溶液中KCl的平均活度系数及超额自由能,计算的活度系数与实验值之间的标准偏差为±0.006。较高的超额自由能表明该体系有较大的混合效应,同时表明在低浓度下K^+-NO_3离子对也可能发生较强的相互作用。已用简单的循环逼近法求算了KNO_3~0的化学计量缔合常数,其结果可用下列经验公式表示: LnK~*=a+bI_e已求得在海水离子强度(I_c=0.68)下KNO_3~0之K~*=2.4,用外推法求得25℃时KNO_3~0的热力学缔合常数值K_a=0.40。
We have determined the mean molal activity coefficients of KCL in KCL-KNO.0 aqueous solutions at constant ion strength ( 1= 0.1, 0.3,0. 5,and 0.7) at 25℃ by measuring the e.m.f. of cells without linquid junctions. We have found that the relationships between the logarithm of the mean activity coefficients of KCL and the concentration of KNO3 in the above mixtures can be described by the following equation: Lgr1± - Lgr10± - a12m2-±12m22. The Harned coefficients a12 and ±12 at each ion strength have been computed by the least square method. The mean activity coefficients of KCL and the excess Gibbs energies of the mixed salts solutions were evaluated by the Pitzer equations. The experiment values of the activity coefficients of KCL were compared with those from the Pitzer equation. The standard deviation is ± 0.006. The relative higher excess Gibbs energies show larger mixing effectes and it may be shown that for the K+-NO3- ion pairs stronger interactions may take place at lower concentrations. The stoichiometric association constants of KNO30 were calculated by a simple iterative process. The results were fit into an empirical equation of the form LnK=a+bIe.. The stoichiometric association constans tf KNO30 obtained from these equations is 2.4 at the ionic strength of sea water (Ie= 0.68) , and the thermodynamic association constant of KNO30 obtained by extrapolating the stoichiometric association constant to infinte dilution is 0.40 at 25℃.
关键词
氯化钾
硝酸钾
活度系数
缔合常数
Potassium Chloride
Potassium nitrate
activity coefficient
association constant
